A power supply loop is set in a cabinet in an equipment room in the telecom industry, and an alarm requirement is imposed on the power supply loop. Currently, a majority of operators in North America such as AT&T, Verizon, Quest, and TWC adopt an alarm fuse, and require that the alarm fuse can display an alarm after a main fuse is blown in a dual-combined-path power supply scenario, which is the “AT&T TP76450/76200 (Issue13/Issue15a 2010.10 latest version)” standard. Therefore, it is unavoidable for equipment providers in the North America market to solve an alarm fuse problem in a dual-combined-path power supply scenario.
However, an existing fuse alarm circuit is mainly designed for a single-path power supply. All fuse vendors can enable an alarm fuse to be blown to indicate an alarm after a main fuse is blown. However, in a dual-combined-path power supply scenario, if fuses (a main fuse and an alarm fuse) are directly connected to a load by using power access modules (power access module A and power access module B), as shown in FIG. 1, because impedance of the main fuse and impedance of the alarm fuse are not at the same order of magnitude, after the main fuse in one path (A1) is blown (Empty), only a small part of device current (such as a 5 A current) passes through the alarm fuse, and a most part of the device current passes through the main fuse in another path (B1). Consequently, a current in the main fuse in B1 approaches 10 A, and only a current that is approximately less than 0.1 A passes through the alarm fuse in A1. As a result, after the main fuse is blown, no alarm prompt is provided because the alarm fuse cannot be blown, which seriously affects reliability of running of a power supply loop.